Releasably securable mechanical fastening systems are well known in the art. Such fastening systems are commonly used to secure two articles together. The fastening system has a substrate and at least one prong comprising a base, shank and engaging means. The prong is joined to the substrate at the base. Contiguous with the base of the prong is the shank, which projects outwardly from the base and substrate. Joined to the shank in spaced relation from the substrate is the engaging means. The engaging means projects laterally from the periphery of the shank and has a surface facing towards the substrate.
Securing of the two articles is accomplished by the engaging means intercepting fibers, strands, or induced localized deformations of a complementary receiving surface. When secured together, the physical obstruction, and resulting mechanical interference, between the engaging means of the fastening system and the fibers, strands or localized deformations of the receiving surface prevents release of the two articles until applied separation forces, such as peel and shear, exceed the resistance of the fastening system and receiving surface to such forces.
One of more significant factors determining the resistance to separation forces the fastening system and receiving surface can withstand without release and separation occurring is the included angle of the engaging means. The included angle is the angular deviation of the engaging means from the perpendicular to the substrate which passes through the center of the base of the prong.
A plethora of engaging means are used with presently known refastenable mechanical fastening systems. For example, one well known type of engaging means incorporates hemispherically shaped heads with a planar surface oriented towards the substrate and are typically referred to as being "mushroom-shaped." Such engaging means are generally illustrated in U.S. Pat. No. 4,216,257, issued Aug. 5, 1980 to Schams et al., U.S. Pat. No. 4,338,800, issued July 13, 1982 to Matsuda and European Patent Application Publication No. 0,276,970, filed Jan. 26, 1988 by the Procter & Gamble Company in the name of Scripps. In such embodiments, however, the engaging means have included angles from about 90.degree. to about 165.degree., depending on the orientation of the stem of the prong relative to the substrate.
Another type of mechanical fastening system utilizes prongs which are cut from a loop and are hook shaped, somewhat resembling a candy cane, as illustrated in U.S. Pat. Nos. 3,083,737, issued Apr. 2, 1963 to de Mestral, 3,154,837, issued Nov. 3, 1964 to de Mestral and 3,943,981, issued Mar. 16, 1976 to De Brabander. Hook type fastening systems generally have included angles of about 180.degree. or less, depending upon where the loop used to form the fastening system is cut. Hook-shaped fastening means produced by methods other than the cut loop system are disclosed in U.S. Pat. Nos. 3,629,032, issued Dec. 21, 1971 to Erb and 3,594,863, issued July 27, 1971 to Erb. These fastening means also have included angles of about 180.degree..
Various other structures are also taught as suitable for use as the engaging means of the fastening system. For example, U.S. Pat. Nos. 3,550,837, issued Dec. 29, 1970 to Erb, 3,708,833, issued Jan. 9, 1973 to Ribich et al. and 4,454,183, issued June 12, 1984 to Wollman disclose alternative types of engaging means, none of which have an included angle of greater than 180.degree..
It is an object of this invention to provide a fastening system which more securely engages or intercepts the strands or fibers of the receiving surface to resist applied separation forces. It is also an object of this invention to provide a fastening system having an engaging means with an included angle substantially greater than about 180.degree. and a reentrant segment.